I'm looking to add a bit more fire to my arsenal and purchase my first wide angle lens. I'm a bit confused as to the quality of some of these lenses though, and could use some advice as to which lens will give me the best bang for the buck.

I'm looking at the EF 28mm f/2.8 ($350), EF 28mm f/1.8 USM ($650), and EF 24mm f/2.8 ($550). All prices are from a local camera shop.

Before going into the specifics on each lens, I just want to make sure I'm correct with my coverage assumption. I'm using an EOS600D, which would have a crop factor of 1.6. Since these models aren't designated by an EF-S, the effective focal lengths for the above would be 44.8mm and 38.4mm on my camera, correct? It seems like none of Canon's wide angle lenses compensate for the smaller frame cameras, since none of the lineup on Canon's site are an EF-S model.

Now for the comparisons. First, with both of the 28mm lenses, the price just about doubles for the larger aperture. I like to have dramatic focusing when I take shots, but is this larger aperture really worth paying almost double for the same focal length? I know that the 1.8 will give me a larger depth of field and will take better shots in low light situations, but will it be that big of a difference to justify paying double the price?

Also...the USM factor. I'm really new to photography, and every time I've gone out I've kept my lenses on manual focus. I feel like a lot of times, the auto-focus doesn't always focus the subject how I want it focused, and I also just enjoy the manual focus more. Makes me feel like I'm doing more than just pointing and clicking. That being said, since the USM really just applies to the auto-focus feature, is it really worth it to spend extra for a function I would rarely use? I've also read a review stating that even though the f/2.8 has a conventional motor, the AF is actually quite fast.

Now with the 24mm, I know I'll be able to get a bit more of the scene into my shots. Comparing the lenses by price though, would it be worth it to spend the extra $200 for a bit wider of a lens with the same f-ratio, or $100 less for the wider lens and less of a maximum aperture?

Ok, and now for the real newbie question. Does a wide angle lens with max apertures like the ones above usually have a smaller minimum? This won't have any effect on my decision, its just more out of curiosity.

I'm not really looking to spend a ton of money here, but at the same time, I'm worried that if I do decide to go with the 28 f2.8, I may regret not spending the extra cash on a much better quality lens. All of your suggestions will be greatly appreciated, and thanks for bearing with this novel!

Thanks for the advice Thomas. My kit lens is indeed 18-55, and since I'm looking for a nice landscape lens for my travels, the ultra wide will be the lens to go for. I didn't even think about the cropped body until I started writing the original post. I appreciate the help man!